Honestly, as a Rogue it is pretty hard to beat a WW Monk 1v1. I will say that in my experience, Rogues are one of the easiest classes to beat as a WW Monk.

You guys work better when you're in a team fight because a lot of your abilities are tailored to being fast, hard-hitting, vanishing, and doing it all over again or resetting it on a new person. In a 1v1, Rogues don't put out flat damage like Warriors or WW Monks do. Therefore, you guys don't really do well against those kinds of classes in duels.

Basically, duels don't mean squat in this game. Rogues are fine in Arenas and in RBGs, but you have to understand the playstyle and then play to its strengths.

Run paralytic poison, force karma with either sdance or shadow blades (be sure you have slice and dice up always, specially for shadow blades) gouge when he karmas, then blind (if he trinkets this it'll be amazing for you) los for restealth, when karma is over use the cool down that you didn't use and go in for the kill.